The present invention relates to an air compressor and, more particularly, to an air compressor control system, which controls pumping action subject to the air pressure status of the accumulation tank, and prevents a big starting current when starting the motor.
Conventional air compressor control systems include two types, namely, the power-interruption type air compressor control system and the uninterrupted type air compressor control system. The power-interruption type air compressor control system, as shown in FIG. 1, comprises a motor M, a pump P, an accumulation tank 1, a circuit breaker (or relay) 2 connected between the motor M and AC power supply, and a pressure switch 3 connected between the accumulation tank 1 and the circuit breaker 2. When the air pressure of the accumulation tank 1 dropped below the predetermined low level, the pressure switch 3 switches on the circuit breaker 2 to start the motor M, thereby causing the pump P to pump forced air into the accumulation tank 1. On the contrary, when the air pressure of the accumulation tank 1 surpassed the predetermined high level, the pressure switch 3 switches off the circuit breaker 2 to stop the motor M, and therefore the pump P is off. This design of power-interruption type air compressor control system has numerous drawbacks as outlined hereinafter:
1. When starting the motor M, a big starting current is produced, which may cause the circuit to trip off or to be burned out.
2. During normal running, power supply is constantly provided to the motor M, i.e., the supply of electricity to the motor M does not vary with the condition of the load. Therefore, this design of power-interruption type air compressor control system does not provide a power saving function.
3. Due to the aforesaid two problems, this design of power-interruption type air compressor control system is suitable for a small scale of air compressor only.
The uninterrupted type air compressor control system, as shown in FIG. 2, comprises a motor M, a pump P, an accumulation tank 1, and a relief valve 4 connected in parallel to the circuit between the pump P and the accumulation tank 1. The relief valve 4 is opened when the pressure of the accumulation tank 1 surpassed the predetermined high level, or closed when the pressure of the accumulation tank 1 dropped below the predetermined low level. When electrically connected to start the motor M, the pump P pumps forced air into the accumulation tank 1. When the pressure of the accumulation tank 1 surpassed the predetermined high level, the relief valve 4 is opened to relieve forced air, and at this time the motor M and the pump P keep running. This design of uninterrupted type air compressor control system has drawbacks as follows:
1. Because the motor M and the pump P keep running when relieving forced air, the motor M and the pump P keep consuming electricity, and much electric energy is wasted. Therefore, this design of uninterrupted type air compressor control system is suitable for high air consumption and high frequency of pumping, but not suitable for low air consumption and low frequency of pumping.
2. Because the motor M and the pump P keep running when relieving forced air, the operational cost of the system is high.
3. Because the motor M and the pump P keep running when relieving forced air, the motor M and the pump P wear quickly with use.
The present invention has been accomplished to provide an air compressor control system, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide an air compressor control system, which saves consumption of electric energy. It is another object of the present invention to provide an air compressor control system, which extends the service life of the motor and the pump. It is still another object of the present invention to provide an air compressor control system, which prevents the occurrence of a big starting current when starting the motor. To achieve these and other objects of the present invention, the air compressor control system comprises a motor, an accumulation tank, a pump, a pressure switch, a pressure control valve, and a micro-controller. The micro-controller is comprised of a CPU (central processing unit), a chopping circuit, a current phase detection circuit, and a voltage phase detection circuit When the pressure of the accumulation tank surpassed a predetermined high level, the pressure switch is off, thereby causing the micro-controller to open the pressure control valve for relieving forced air pressure and then to turn off the motor. When the pressure of the accumulation tank dropped below the predetermined low level, the pressure switch is switched on, thereby causing the micro-controller to provide power supply to the motor again and then to close the air pressure control valve for enabling forced air to be pumped into the accumulation tank by the pump after the motor has been fully started.